Get the Yak, the llama will be too roomy for you. People that get oversize boats for their size usually find them unstable in spashy water.
Yep easy to learn, take it on some mellow rivers first, learn ferrying and back paddling and generally avoiding hitting anything. Sounds like a good trip. Class III with bikes is pushing it
Deck is your call, if warmth is not an issue then you just need to decide how much whitewater you intend to do.